Servlet登录二-带数据库

public class Dao {
    
    public static Connection getConnection()
    {
         try {
                Class.forName("com.mysql.jdbc.Driver");
                String url ="jdbc:mysql://localhost:3306/JavaWeb?useUnicode=true&characterEncoding=utf-8&useSSL=false&allowPublicKeyRetrieval=true";
                Connection con=(Connection) DriverManager.getConnection(url, "root", "AQCTBQLYxingye1.");
                return con;
                } catch (Exception e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
                return null;
            }
    }

    public static void Insertdata(List<Person> l) throws SQLException
    {

        Connection con= getConnection();
        Statement stat = (Statement) con.createStatement();
        stat.executeUpdate("delete from user");
        for(Person p:l) {
            String str= "insert into user values(‘"+p.getZh()+"‘,‘"+p.getMm()+"‘)";
             System.out.println(str);
             stat.executeUpdate(str);
        }
        stat.close();
        con.close();
    }
    public static List<Person> Selectdata(String param) throws SQLException
    { 
        List<Person> list=new ArrayList<>();
        
        Connection con= getConnection();
        Statement stat = (Statement) con.createStatement();
        String sql="select *from user";
        sql+=" where  zh=‘"+param+"‘";
        
        ResultSet result = stat.executeQuery(sql);
        list.clear();
        while (result.next())
        {
             Person p=new Person(result.getString("zh"),result.getString("mm"));
             list.add(p);
        }
        stat.close();
        con.close();
        return list;
        
    }
    
    
}

public class LoginServlet extends HttpServlet {

    @Override
    public void init() throws ServletException {
        // TODO Auto-generated method stub
        super.init();
        List<Person> l=new ArrayList<>();
        Person p=new Person("root","admin");
        l.add(p);
        p=new Person("123","123");
        l.add(p);
        try {
            Dao.Insertdata(l);
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String zh=req.getParameter("zh");
        String mm=req.getParameter("mm");
        String info=null;
        try {
            List<Person> l=Dao.Selectdata(zh);
            if(l.size()==0) {
                    info="该用户不存在";
            }
            else {
                if(l.get(0).getMm().equals(mm)) {
                    info="登录成功:账号"+zh+"  -密码:"+mm;
                }
                else {
                    info="密码错误";
                }
            }
            
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
            info=e.getMessage();
            
        }
        req.getSession(true).setAttribute("info",info);
        resp.sendRedirect(req.getContextPath()+"/"+"info.jsp");
        
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(req, resp);
    }

    
}